Most of the coding region was replaced with a cre gene and a neomycin cassette. The cre gene sequence was fused in-frame following the first 13 codons of the gene. The endogenous promoter is active in telencephalon, anterior optic vesicle, otic vesicle, facial and head ectoderm, olfactory epithelium, mid-hindbrain junction and pharyngeal pouches.